Applications for wireless systems capable of tracking vehicles and people all over the planet are only beginning to be realized. Companies seeking to tap the commercial potential of these technologies are installing wireless location devices in vehicles, hand-held computers, cell phones, and even watchbands. Scientists have even developed a chip that can be implanted beneath the skin.
Many location systems use the satellite-based Global Positioning System (GPS). This technology has been available for some time for airplanes, boats, cars, and hikers. But companies have only recently begun manufacturing GPS chips that can be embedded in wireless communications devices. GPS uses satellite signals to determine geographic coordinates that indicate where the person with the receiving device is situated.
Other location systems use cellular telephone technology. These devices are typically embedded into cellular telephones, and require both sending and receiving capability. For example, U.S. Pat. No. 5,646,632 describes a technique based on CDMA cellular telephone signals. It requires a transmitter as well as a receiver in the location device, and is dependent on a fixed known time offset between synchronization transmissions.